Known in the art is a method for producing fractions of paraffin hydrocarbons of the isostructure, including C.sub.4 -C.sub.7 fractions, by alkylating paraffin hydrocarbons with olefins of the isostructure in the presence of a catalyst such as concentrated sulphuric acid and hydrogen fluoride.
The alkylate comprising isoparaffin hydrocarbons has an octane number of 90-92 according to the motor method in a pure form. However, the catalyst used in the known method causes corrosion of the process equipment, and is toxic. In addition, the initial raw material resources are limited.
Known in the art is a method for producing fractions of paraffin hydrocarbons of the C.sub.4 -C.sub.7 isostructure by means of hydroisomerization of a light straight run gasoline fraction, boiling out at a temperature to 62.degree. C., on bifunctional catalysts constituted by noble metals, such as platinum and palladium, applied to aluminium oxide at a temperature of 400.degree.-480.degree. C.
Said method is characterized by high temperatures, which adversely affects the thermodynamic balance of the process and thereby makes it impossible to obtain a target product with a sufficiently high octane number (the octane number does not exceed 79-80 according to the motor method in a pure form). In addition, the insufficiently high conversion of the initial raw material into isoparaffins makes it necessary to recirculate the unconverted raw material, which complicates the flow sheet as a whole. Another disadvantage of the method lies in limited resources of the initial raw material.
The method described above can also be carried out in the presence of similar catalysts, but halogenated beforehand, which improves their activity and makes it possible to carry out the process at lower temperatures, namely, 100.degree.-250.degree. C.
This method makes it possible to obtain a fraction of paraffin hydrocarbons of the C.sub.4 -C.sub.7 isostructure with a higher octane number (80-85, according to the motor method in a pure form). However, the catalysts used in this method are aggressive, cause intensive corrosion of the process equipment, and become rapidly deactivated.
Also known in the art is a method for producing fractions of paraffin hydrocarbons of the C.sub.4 -C.sub.7 isostructure by hydroisomerization of the gasoline fraction of catalytic cracking, boiling out at 100.degree. C., in the presence of hydrogen on a catalyst constituted by amorphous nickelalumosilicate, at a temperature of 200.degree.-400.degree. C., under a pressure of 40-120 atm. and at a space rate of feeding the gasoline fraction of 0.5-1.5 hour.sup.-1.
The catalyst used in the above method does not make it possible to produce a target fraction with a sufficiently high octane number (the octane number does not exceed 83 according to the motor method in a pure form). In addition, the insufficiently high conversion of the initial raw material into isoparaffins makes it necessary to recirculate the unconverted raw material. Hydroisomerization at higher pressures (40-120 atm.) complicates the technology and equipment.